Controlling system in protective devices of photocell type for presses and the like

ABSTRACT

A control system for presses and the like of the type having a path for insertion and removal of work pieces includes a motor operated protective shutter insertable into the work piece insertion and removal path and a photocell system defining a light controlled area arranged transversely across such path and on the operator&#39;&#39;s side of the shutter. Circuitry responsive to the condition of the photocell device controls operation of the shutter motor. Press releasing circuitry, actuable to permit initiation of a press cycle, is controlled by contacts actuable by the shutter and by timing circuitry. Operation of the timing circuitry is initiated when the light controlled area, or light curtain, becomes unoccupied, the timing circuitry operating for a short time within which the shutter initiates and completes its closing movement. Then, the press is released for initiating a press cycle, in response to the contacts sensing the closed position of the shutter and in cooperation with the timing circuitry.

[ Oct. 7, 1975 United States Patent Svensson [54] CONTROLLING SYSTEM INPROTECTIVE Primary Examiner-Bcnjamin Dobeck DEVICES OF PHOTOCELL TYPEFOR PRESSES AND THE LIKE Attorney, Agent, or FirmWoodhams, Blanchard &Flynn [75] lnventor: Lars Erik Svensson, Tullinge,

Sweden [57] ABSTRACT A control system for presses and the like of thetype [73] Assignee: Safer Marketing Aktiebolag,

Stockholm, Sweden having a path for insertion and removal of work piecesincludes a motor operated protective shutter insert Dec. 18, 1973 [22]Filed: able into the work piece insertion and removal path [21 1 and aphotocell system defining a light controlled area Appl. No.: 425,913

arranged transversely across such path and on the operators side of theshutter. Circuitry responsive to the [30] Forelgn Apphcauon Pnonty Datacondition of the photocell device controls operation of 1972 16833/72the shutter motor. Press releasing circuitry, actuable to permitinitiation of a press cycle, is controlled by contacts actuable by theshutter and by timing cir- [52] US. Cl. 318/480; 318/484; 317/124 Int.

GOZF HOZH cuitry. Operation of the timing circuitry is initiated Fieldof when the light controlled area, or light curtain, be-

125 comes unoccupied, the timing circuitry operating for a short timewithin which the shutter initiates and com- References Cited pletes itsclosing movement. Then, the press is re- UNITED STATES PATENTS lU/l97lleased for initiating a press cycle, in response to the 3 612 884Linardosm"Hmnmmmu" 7/124 X contacts sensing the closed position of theshutter and in cooperation with the timing circuitry.

11 Claims, 5 Drawing Figures US. Patent Oct. 7,1975 Sheet 2 of 53,911,344

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[BEE-l U.S. Patent Oct. 7,1975 Sheet 3 of5 3,911,344

U.S. atent Oct. 7,1975 Sheet 4 of5 3,911,344

mm m 4m Q Arm Q NU m 1 4 Ni m m H m n L m ,2 a llllllllllllllllll l i umm m L T n 51' n w i m 1 v u L m u "I 1 1 l. m k m B a rlllfilllallh Y PiCONTROLLING SYSTEM IN PROTECTIVE DEVICES OF PI-IOTOCELL TYPE FOR PRESSESAND THE LIKE The present invention refers to a controlling system inprotective devices of photocell type for presses and the like.

It has previously been proposed to arrange protective devices forpresses and the like comprising a so-called light curtain, i.e. aphotocell arrangement comprising a plurality of light tracks in front ofthe place where the working pieces are to be inserted and taken out fromthe press during work, as well as a protective shutter adapted to closesaid path of introduction and removal while the press is performing itsworking stroke. In order to increase the safety in systems of the typehere in question it is necessary to automatize to the utmost extent theoperation of the press so that the operator will not unnecessarily beconcerned with a plurality of controlling steps for every working stroketo be performed by the press. By reducing the number of workingoperations for every working stroke an automatic increase in safety isobtained and the operator will be able to concentrate on the workingstep itself, i.e. to cause the working pieces in question to arrive atthe proper place and in correct position in the press and the pressingoperation to be correctly performed. In an arrangement according to thepresent invention the operator only needs to introduce and remove theworking pieces to be worked into and from the press along the prescribedpaths of insertion and removal, the protective device automaticallyoperating the press in such a way that when the path in question is freefrom foreign objects and hands the press will be automatically started.In order to provide absolute safety in such a device, however, a systemcomprising mutually cooperating devices is required.

The characterizing features of the present invention appear from theattached claims. The invention will be more closely described byreference to an embodiment shown in the attached drawings in asimplified sche matic way. The various FIGS. 1 to show the system invarious positions of operation, wherein:

FIG. 1 diagrammatically discloses the system embodying the invention inan initial operational state, wherein the protective shutter S is liftedto free the path through the light curtain L for insertion or removal ofa work piece therethrough and wherein the press is in its startingposition.

FIG. 2 is a view similar to FIG. 1 but showing the system in asubsequent state resulting from insertion of an object into the lightcurtain L.

FIG. 3 is a view similar to FIG. 2 but showing the system in asubsequent state, following removal of such object and the resultantclosure of the shutter S and starting of the press.

FIG. 4 is a view similar to FIG. 3 but showing the system in asubsequent state wherein an object has again been inserted into thelight curtain L, resulting in stopping of the press.

FIG. 5 is a view similar to FIG. 3 but showing the system in asubsequent state near the end of the press cycle and wherein the controlcircuit to the press is broken to cause the press to stop.

In all the drawings the press itself is only represented by a cam disc Pdriven by the press and adapted, during the operation of the press, torotate in the direction of the arrow P. The cam disc P is adapted tooperate two contact means to be described later. The protective deviceproper is represented by a light curtain device L with light beamsindicated by broken lines. The light curtain is provided at the path forinserting and removing work pieces in the press. Immediately behind thepath seen from the operator there is provided a protective shutter Swhich is movable up and down for respectively exposing and closing thesaid path for insertion and removal of work pieces into and from thepress. The protective shutter S is adapted to be driven by a linearmotor having the general designation M. The protective shutter S isguided in guides SG provided with cams N1, N2 and N3 adapted tocooperate with contact means G1, G2, G3 respectively. The lastmentionedcontact means comprise a plurality of break and make contacts and foridentification of these contacts in the surrounding schematicrepresentation, in all the Figures the first contact of for examplecontact means G1 is designated as G11, its second contact as G12 and itsthird contact as G13 and in correspondence thereto the first contact ofcontact means G2 as G21, the second contact as G22 etc. This system ofidentifying the contacts is used throughout the specification also asfar as contact groups belonging to relays areconcerned. Two contactmeans G4 and G5, the contact groups of which in an analogous way can betraced in the schematic representation, cooperate with cam disc P.

Between the poles, here designated as O and of an alternating currentmains there is connected a circuit for controlling the linear motor Madapted to drive the protective shutter 1 up and down. The phasecontacts of the motor are designated X, Y, Z and provided within thebroken-line rectangle on the left side of the Figures. The motor is suchthat it can operate in opposed working directions depending on theconnection of its phase capacitor FC to the contacts X or Y. To cut-inthe motor in different driving directions a contact B3 is provided in acontact group belonging to a relay B to be described later on, thatcontact providing insertion of the phase capacitor FC between one poleof the mains and the pole clamp X while at the same time the pole clampY is in direct connection with the last-mentioned mains pole or viceversa. Contact Z is continuously connected to the other mains pole O. Inthe position shown in FIG. 1 shutter S is in its upper position, i.e.the linear motor pulls the shutter upwardly and the opening through thelight curtain L is exposed. In order to reverse the driving direction ofmotor M it is only necessary to reverse contact B3 whereby the poleclamp X of the motor will be directly connected to the one pole of thealternating current mains via a contact K1 to be described later on, thecapacitor FC being connected between said alternating current pole andthe pole contact Y on the motor. Three other contacts are also providedin the motor circuit viz. contacts C2 and D2 belonging to contact groupsin relays C and D and a contact K2 belonging to a manual correctivebutton K as well as a contact G51.

Also connected to the alternating current mains is a transformer thesecondary of which feeds a rectifier circuit to form together a netunit, or dc. current supply, designated as DC. Said net unit feeds relaycircuits and electronic circuits with current. The minus pole of netunit DC is connected to so-called protective earth, or groundT-Ewhereasthe positive pole is connected to the current supply for the relaycircuits. Within a broken-line rectangle to the right of net unit DCthere is shown a photocell amplifier circuit F which is in directconnection with the light curtain L and the contact function of which issymbolically indicated by a contact Fl. In connection with the net unitthere are provided relays A, B, C and D with their contact groupsdesignated A1, A2, A3, B1, B2 etc. Moreover, there are provided in saidcircuits current limiting resistors R1, R2, R3, R4, R5 and capacitorsE1, E2, E3, E4 as well diodes HI and H2. The various relays aswell asthe connection of the contacts and their mutual cooperation will be mostsimply described by describing the functional processes occurring duringdifferent states of operation. In order to facilitate the study of theFigures those conductors which in an illustrated state of operation donot conduct current have been shown in broken lines.

FIG. 1 shows a state of operation of the protective device in which theprotective shutter S is lifted and the passage through the light curtainL is thus free to insert or remove one work piece therethrough. Thepress is in the starting position as indicated by the cam disc P whichis directly connected to the press. Here, it will be seen that controlcircuits for linear motor M are in such a contact position that theprotective shutter 1 is held D3, resistor R3, contact A2 and contact A3.It is to be.

noted that all relays in the actual condition are inactive. In thisposition the press still cannot be started, because contacts Cl and D1are in their. inoperative positions and thus only close the supervisingcircuit T. Also, the

I protective shutter S cannot be lowered to closed posiin the liftedposition. Contact member G5 contributes thereto by its cooperation withcam P" whereby the contact thereof G51 is held in closed position andforms, as previously mentioned, a link in the motor circuit to theprotective shutter. In respect to the fact that the light curtain L isunbroken the photocells thereof (not shown) are actuated, the electricalsignals derived therefrom being amplified in thc photocell amplifier F,thereby to obtain such a contact function that a closure is obtainedthrough F1, whereby the circuit of relay A is closed and relay A isactuated. The circuit connected to relay A comprises resistor R2 andcapacitor E2 which are connected in series between plus and minus in theconductors coming from DC. When contact function F1 is broken, capacitorE2 will be charged to full direct voltage through resistor R2. Whencontact function F] is closed there will be full voltage supply throughcapacitor E2 over the relay coil belonging to A. Thereby E2 will bedischarged through the relay coil causing the relay to operate. ResistorR2 is so chosen as to adequately supply relay A with holding current butnot to be able to cause the relay to operate. The state as describedcauses all the relevant contacts Al, A2 and A3 to be in their actuatedpositions. In the state shown in FIG. 1, the circuits to all relay coilsB, C and D are broken thereby causing the respective contacts C1 and D1to be in their inactive positions, a supervising circuit T beingconnected indicating that no operation can be performed. The controlcircuit U for the press machine is fully disconnected.

Thus, in this position the press cannot start because both relays C andD are inactive. Both these relays must be actuated to enable the controlcircuit U to be closed by means of contacts C1, D1.

If a hand HA, FIG. 2, is now inserted into the light curtain L theoutgoing signals from the photocell device will be changed immediately,the photocell amplifier reacting in such a way that the closing of thecontact at F1 ceases thereby disabling relay A. The consequence thereofis that the capacitor El will be charged via resistor R1 and contact A2.Also capacitor E3 will be charged via contacts G52, G12, G22, C3,

tion because the driving direction of motor M is such as to hold shutterS in the elevated position.

If now hand HA is removed from the light curtain L as in FIG. 3, thefollowing actions will take place. Due to the fact that the photocellsnow again are fed by the full light curtain flow such signals areobtained to the photocell amplifier F that the contact function Fl againis closed whereby relay A is actuated. This has the consequence that astate of contact actuation similar to FIG. 1 is obtained. However,during the time under which the hand has been within the light curtainthe capacitor El has been charged and due to the actuated position ofcontact A2, discharge current now flows from capacitor E1 through thecoil of relay B via contact G41 to ground. Hereby relay B will beactuated and holding current will be supplied to the relay via itscontact Bl,compare FIG. 3. By its transition to the actuated positioncontact B2, initially, will not bring about any change in current flowwhereas the reversal of contact B3 reverses the direction of rotation ofthe linear motor M so that the protective shutter S will be lowered.This lowering of the protective shutter has several consequences.Contact members G1 and G2 will cooperate with cams N1 and N2, thecontact groups comprised by these contact members thereby changingposition. Contact member G3 will be brought out of engagement with camN3 so that also its contacts will change position. The immediateconsequence thereof will be that the previously charged capacitor E3will discharge its discharge current through contact A3, diode H2 andthe now series-connected closed contacts G21 and G11 to theparallel-connected coils of relays C and D. After actuation of theserelays a holding current chain for the relays is prepared comprisingcontacts A1, G43, B2, D3, C3 and contacts G11, G21. However, no holdingcurrent is obtained prior to the press being started and rotation of camdisc P to such an extent that cam P" is disengaged from contact G5whereby contact G53 thereof will close the holding current circuit for Cand D. By closing relays C and D also contacts Cl and D1 are closedwhereby the control circuit U of the press is closed and the pressstarts. As soon as cam P" on cam disc P comes out of engagement withcontact member G5, contact G51 will be broken which means that if forsome reason the press would stop in the position illustrated in FIG. 3the protective shutter S cannot be caused to open even if relay B forsome reason should be released so that contact B3 would be reversed.Normally, in the state illustrated in FIG. 3 the protective shutter S isheld by motor torque in the closed position because relay B all the timeis actuated. In the state illustrated in FIG. 3 all relays are actuated.Capacitor E2 is connected in parallel over relay coil A via currentlimiting resistor R2 but does not receive any substantial chargingvoltage.

If for some reason hand HA is introduced into the light curtain L in thestate illustrated in FIG. 3 in a way as shown in FIG. 4 the followingactionswill take place. The photocells cooperating with the lightcurtain L will not emit any'control signals to the photocell amplifierF, thus breaking the contact function F1 and causing the relay A todrop. Hereby, contact AI will drop causing the holding current to relaysC and D to cease and the relays to drop. When relays C and D dropcontacts Cl and D1 will interrupt the control circuit U of the press andclose the supervising circuit T causing the press to stop. Relay 8 isstill actuated which means that via contact B3 the linear motor M is fedso that shutter S is maintained in the closed position. Thereby, theoperator is prevented from inserting the hands into the region about thework piece without specific measures while in such a case the workingstroke of the press has been interrupted. As appears from the circuitdiagram in FIG. 4 capacitor E2 will be charged in this state to its fullvoltage by the current limiting resistor R2. Moreover, capacitor E1 willbe charged via current limiting resistor R1 and contact A2. In contrast,capacitor E3 will be discharged through the circuit formed by contactsA3, resistor R3, contact D3, C3, resistor R5, contact D3, C3, resistorR5 and contact G31 to ground. This is a safety measure taken because thepress shall not be operable again from its interrupted position withoutspecific measures when the hand is removed from the light curtain. Asappears from the circuit diagram, upon removal of hand HA from the lightcurtain relay A will again be actuated whereby contact A3 connectscapacitor E3 with the coils of relays C and D.

In order to get, in this position, access to and to adjust the workpiece that may have come into a faulty position, the protective shutterS must be elevated to permit free passage through the light curtain.Such an operation can be performed by pressing the so-called correctivebutton K while simultaneously the hand HA is within the light curtain.The contacts K1, K2 and K3 of the corrective button K are herebyreversed causing contact Kl to break the current to linear motor Mholding the protective shutter in closed position whereas a contact K2via the dropped relay contacts C2 and D2 connects the linear motor M tothe mains in such a way that shutter S is lifted. As soon as protectiveshutter S started its upward movement contact members G1 and G2 will bedisengaged from cams N1 and N2 and subsequently contact member G3 willstart cooperation with cams N3. Due to this contact reversal contactsG11 and G2] will break the connection to relays C and D thus eliminatingany possibility to start the press (contacts C l and D1 connected to thesupervising circuit T). The reversal of contacts G12 and G22 means nochange in the current flows. However, G31 breaks the discharge currentpath for capacitor E3. This capacitor, however, is fully dischargedunder the present conditions. Contact K3 now causes a current path to beestablished through contact A1 so that capacitor E4 is charged throughcurrent limiting resistor R4. The contact positions just described aredesignated by dotted marks both concerning contacts and current paths.The operator now can freely handle the work piece without risk of pressoperation and personal injury caused thereby.

After having performed the adjustment the operator only needs towithdraw the hand from the light curtain and to release the correctivebutton to cause the press to start again. During this last-mentionedoperation the following coupling sequence will take place. By removal ofthe hand from the light curtain the photocell device will emit signalsand causes the contact function F1 to be closed so that relay A isactuated by a current impulse received from capacitor E2 in this phase,however, the actuation of relay A does not entail any immediate changein current flows. However, the reversal of contacts K1 and K2 entails areversed connection of linear motor M causing protective shutter Simmediately to be shifted down to closing position. Hereby, contactmembers G1 and G2 will come into cooperation with cams N1 and N2causing, among others, contacts G11 and G21 D close. Due to the chargebrought about during closing of contacts K3 in capacitor E4, there isnow a direct discharge current path via diode H1 and contacts G21 andG1] to relays C and D which will be actuated and, in a way describedabove, cause the press to start (contacts C1 and D1 close the controlcircuit U of the press).

After the above described operation the press will continue its workingstroke while simultaneously the cam disc P will rotate in the directionof the arrow P.

When the press movement has continued so far that cam P" comes intocooperation with contact member G4 the following action takes place.Contact G4] interrupts the holding current path through relay B which isreleased. Thereby, also the holding current paths to relays C and D areinterrupted due to the fact that contact B2 is transferred to itsdisengaged position. Already before relay B drop's, the holding currentpath to relays C and D has been broken by contact G43. Hereby, alsorelays C and cl will be disengaged and contact group C1, D1 breaks thecontrol circuit to the press which is stopped. As a safety measurecapacitor E3 is connected by contact A3 to ground via contact G42 in thestate as described. During the lastmentioned action the brake mechanismsof the press are actuated to bring the press to a correct stoppingposition and starting position after some additional movementcorresponding to a rotation of cam disc P so that cam P" again comesinto contact with contact element G5. Hereby, a starting position asshown in FIG. 1 is obtained. It is to be noted that when relay B isdisengaged and drops contact B3 breaks the connection between the linearmotor M and the mains. The protective shutter, however, remains in itsclosed position due to gravity. This brief moment in the final phase ofthe working stroke of the press is considered as undangerous from thesafety point of view so that the current to the linear motor in thiscase can be disconnected during the period in question. As soon as thecam P comes into engagement with contact element G5 contact G51 is againclosed connecting the linear motor so to the mains that the protectiveshutter S is lifted whereby the starting position according to FIG. 1 isagain reached.

As will clearly appear from the above description a particularlyefficient protective system is obtained by the arrangement according tothe present invention also permitting an extremely simple control of thepress by the operator. The construction offers, among others, thefollowing advantages which efficiently contribute to the safety obtainedwith the device in question. In order to initiate a press movement theoperator only has to pull out his hand from contact with the lightcurtain L whereafter the press performs a complete working strokewithout further measures. If during the working stroke of the press theoperator introduces his hand into the light curtain the press will bestopped but the protective shutter will remain blocked againstmechanical opening due to the fact that the linear motor is connected tothe mains with such a driving direction that the protective shutter S isheld closed. Only after depression of the corrective button K while thehand simultaneously is maintained within the light curtain theprotective shutter S can be brought to open position for any necessaryadjustment of the work piece. During this action the press is fullylocked against unintentional start because the control releasing relaysC and D cannot supply any operating current due to the fact that amongothers the series-connected contacts G11 and G21 both are open. As soonas the operator removes his hand from the light curtain and releases thecorrective button K the press will start immediately and continue itsworking stroke without additional measures taken by the operator. It isto be noted that if the press has been stopped by insertion of the handHA in the light curtain as shown in FIG. 4 no new starting impulse canbe obtained unless both the corrective button K has been actuated andthe hand HA has been removed from the light curtain L. A new startingpulse in the position illustrated in FIG. 4 can be obtained only by thecharging voltage received by capacitor E4 during depression of contactK3 of the corrective button. A current path which in a conventional waycan charge capacitor E3 for normal start does not exist in this case.

Also a safeguard against inter circuit faults is enclosed in the system.If for some reason relays C and D will not be actuated within a certainprescribed interval of time the actuating current pulse will ceasebecause capacitor E3 is so dimensioned that its energy content at agiven charging voltage is exactly sufficient for a normal actuation ofsaid relays C and D. This requirement is also valid for the rest of thecapacitors E1, E2 and E4 because if for some reason the relays to beactuated by these capacitors do not operate immediately there shall beno actuating current on these relays which thereby are prevented frombeing actuated accidentally at times when they could cause the press tostart under faulty conditions. By such an arrangement of capacitors forobtaining actuating pulses for relays an indirect supervision of thecorrectness of the relay function is obtained whereby the actuatingtimes are held within tolerance limits. Moreover, such safety is alsoobtained in that the protective shutter must be in the closed positionin order to enable the operating relays C and D of the press to beactuated, which means that contacts G1 and G2] must be closedsimultaneously. Moreover, the press will not start if, for example, onlyrelay C would be actuated because then only contact Cl would be in theclosed position, leaving the control circuit U still open. Moreover, theholding current circuit for relays C and D comprises seriesconnectedcontacts C3, D3 from the respective relay contact groups.

Finally, in case of a current interruption in the circuit shown in theFigures, the press cannot be started even if there is current present atthe press control means, because the control circuit U of the press isinterrupted as long as relays C and D are disabled due to the respectivecontacts Cl and D1. It is also not possible to inadvertently start thepress if there is current charge on all control circuits but not on thedriving motor of the press, which means that even if the circuits shouldreach the starting condition by removal of the hand HA in FIG. 2, asubsequent supply of driving current to the press would not cause thepress to start because the actuating pulse time for relays C and D thenhas expired already a long time ago without a movement of cam disc P andwithout closure of the holding current circuit for the respective relaysC and D by, among others, contact G53.

In the specification and claims it is stated that a socalled lightcurtain is to be used in connection with the system described. However,other equivalent arrangements such as capacitive feeling devices can beused. Moreover, reference has been made throughout to relays. However,this term is intended to comprise equivalent means such as electronicswitches and the like.

What I claim is:

l. A control system for operating presses and the like of the typehaving a path for insertion and removal of work pieces, comprising:

a motor operated protective shutter moveable into and out of said workpiece insertion and removal a light curtain incorporating a photocelldevice and defining alight controlled area transversely in said path andon the operators side of said shutter;

shutter circuit means connected to and controlled by said photocelldevice for initiating operation of the shutter motor to close saidshutter;

shutter contact means actuable by said shutter upon such closurethereof;

press releasing circuit means responsive to said actuation of saidshutter contact means for starting said press;

timing means in circuit with said shutter circuit means and actuableupon said removal of an interrupting object from said light curtain fortiming a short period of time during which closure of said shutter mustbe initiated;

and further timing means in circuit with said press releasing circuitmeans for timing a period during which press operation must beinitiated.

2. Control system as claimed in claim 1, in which said timing meanscomprises capacitors, and including relay means coupled to saidphotocell device and (1) disabled thereby when the light curtain isbroken for causing said capacitors to be charged and (2) actuatedthereby when the light curtain becomes unbroken for permitting dischargeof said capacitors to said circuit shutter means so as to close theshutter, and then to said press releasing circuit means so as to startsaid press, said time periods being the discharge times of saidcapacitors.

3. A control system for operating presses and the like of the typehaving a path along which work pieces are insertable and removable by anoperator, comprising:

a motor operated protective shutter moveable for blocking and unblockingthe work piece insertion and removal path;

light curtain means disposed transversely of said path and on theoperators side of said shutter and including photocell means responsiveto objects inserted through the light curtain; I

contact means actuable by said shutter upon opening and closing of theshutter;

start pulse circuit means actuable for initiating a press startingsequence in response to at least partial interruption of said lightcurtain by an object and responsive to a subsequent removal of theinterrupting object from the light curtain for changing state, saidstart pulse circuit means being coupled to and actuated by saidphotocell means;

shutter control circuit means actuable in response to said change ofstate of said start pulse circuit means for initiating closing saidshutter;

press releasing circuit means coupled to said start pulse circuit meansand contact means and responsive to closing of said shutter forsimultaneously initiating the press stroke;

timing means coupled to said shutter control circuit means and pressreleasing circuit means. respectively, for timing limited time intervalswithin which said control circuit means and press release circuit meansmust carry out said initiations 4. Control system as claimed in claim 3in which said start pulse circuit means include a relay coupled to saidphotocell means and actuable thereby when the light curtain is unbrokenand disabled thereby when the light curtain is broken, said timing meanscomprising capacitors, said control circuit means and press releasingcircuit means including paths coupling respective said capacitors tosaid relay l for charging of said capacitors when said relay is disabledand, upon a subsequent actuation of said relay, (2) for enablingdischarge of current from said capacitors to time said limitedintervals, said shutter control circuit means and press releasingcircuit means including portions coupled to respective said capacitorsfor actuation by the discharge current therefrom.

5. Control system as claimed in claim 3 in which said press releasingcircuit means includes a pair of relays with coils connected inparallel, said relays having contacts, a contact of one said relay beingconnected in series with a contact of the other said relay, the presshaving a press control circuit containing said series contacts andresponsive to closure of both said contacts for operating said press.

6. Control system as claimed in claim 5 in which said contact meansactuable by said shutter include a series pair of shutter contactscloseable and openable with said shutter, said control circuit meansincluding a current path in which said series shutter contacts are inseries with said parallel relay coils, whereby closure of both saidshutter contacts is required for actuation of said relay coils.

7. Control system claimed in claim 6 in which said start pulse circuitmeans includes a relay actuable by said photocell means and havingcontacts, said pair of relays of said press releasing circuit meanshaving respective further contacts in series, said press releasingcircuit means further including a holding current path for said pair ofrelays which includes said series further contacts thereof and furtherincludes a contact of said photocell actuable relay, said controlcircuit means including a further relay responsive to said photocellactuable relay for operating said shutter, means moveable in synchronismwith the working stroke of the press and press stroke contactsassociated therewith for completing said holding current path uponinitiation of the working stroke of the press.

8. Control system as claimed in claim 7 in which said means moveable insynchronism with the working stroke of the press include a furthercontact, said control circuit including a current path to the shuttermotor and containing said last mentioned contact for deenergizing saidshutter motor upon initiation of said working stroke of said press.

9. Control system as claimed in claim 7 including means coupling acontact of said photocell actuable relay in series in said holdingcurrent path of said pair of press releasing circuit means relays forbreaking said holding current path upon interruption of the lightcurtain following starting of the press, whereby to deenergize said pairof press releasing circuit means relays and stop said press.

10. Control system as claimed in claim 9 including a corrective contactmember manually actuable after said stopping of said press and meanscoupling contacts of said corrective contact member in said shuttercontrol circuit means, means defining a charging current path includinga further contact of said manually actuable corrective contact member,said charging current path defining an additional start pulse circuitmeans responsive to deactuation of said manually actuable correctivecontact member and elimination of said light curtain interruption for,simultaneously with a subsequent closing of said shutter, once againapplying operating current through said series pair of shutter contactsto said parallel press releasing circuit means relays to restart thepress after an interruption of press operation by an interruption of thelight curtain.

11. Control system as claimed in claim 10 in which said press releasingcircuit means includes a normal press starting pulse path including acontact of said photocell responsive relay, contacts of said pair ofrelays of said press releasing circuit means, and a contact of saidshutter actuable contact means, said normal starting pulse path beingcoupled to the timing means capacitor associated with said pressreleasing circuit means for discharging said capacitor therethrough.

1. A control system for operating presses and the like of the typehaving a path for insertion and removal of work pieces, comprising: amotor operated protective shutter moveable into and out of said workpiece insertion and removal path; a light curtain incorporating aphotocell device and defining a light controlled area transversely insaid path and on the operator''s side of said shutter; shutter circuitmeans connected to and controlled by said photocell device forinitiatinG operation of the shutter motor to close said shutter; shuttermeans actuable by said shutter upon such closure thereof; pressreleasing circuit means responsive to said actuation of said shuttercontact means for starting said press; timing means in circuit with saidshutter circuit means and actuable upon said removal of an interruptingobject from said light curtain for timing a short period of time duringwhich closure of said shutter must be initiated; and further timingmeans in circuit with said press releasing circuit means for timing aperiod during which press operation must be initiated.
 2. Control systemas claimed in claim 1, in which said timing means comprises capacitors,and including relay means coupled to said photocell device and (1)disabled thereby when the light curtain is broken for causing saidcapacitors to be charged and (2) actuated thereby when the light curtainbecomes unbroken for permitting discharge of said capacitors to saidcircuit means so as to close the shutter, and then to said pressreleasing circuit means so as to start said press, said time periodsbeing the discharge times of said capacitors.
 3. A control system foroperating presses and the like of the type having a path along whichwork pieces are insertable and removable by an operator, comprising: amotor operated protective shutter moveable for blocking and unblockingthe work piece insertion and removal path; light curtain means disposedtransversely of said path and on the operator''s side of said shutterand including photocell means responsive to objects inserted through thelight curtain; contact means actuable by said shutter upon opening andclosing of the shutter; start pulse circuit means actuable forinitiating a press starting sequence in response to at least partialinterruption of said light curtain by an object and responsive to asubsequent removal of the interrupting object from the light curtain forchanging state, said start pulse circuit means being coupled to andactuated by said photocell means; shutter control circuit means actuablein response to said change of state of said start pulse circuit meansfor initiating closing said shutter; press releasing circuit meanscoupled to said start pulse circuit means and contact means andresponsive to closing of said shutter for simultaneously initiating thepress stroke; timing means coupled to said shutter control circuit meansand press releasing circuit means, respectively, for timing limited timeintervals within which said control circuit means and press releasecircuit means must carry out said initiations.
 4. Control system asclaimed in claim 3 in which said start pulse circuit means include arelay coupled to said photocell means and actuable thereby when thelight curtain is unbroken and disabled thereby when the light curtain isbroken, said timing means comprising capacitors, said control circuitmeans and press releasing circuit means including paths couplingrespective said capacitors to said relay (1) for charging of saidcapacitors when said relay is disabled and, upon a subsequent actuationof said relay, (2) for enabling discharge of current from saidcapacitors to time said limited intervals, said shutter control circuitmeans and press releasing circuit means including portions coupled torespective said capacitors for actuation by the discharge currenttherefrom.
 5. Control system as claimed in claim 3 in which said pressreleasing circuit means includes a pair of relays with coils connectedin parallel, said relays having contacts, a contact of one said relaybeing connected in series with a contact of the other said relay, thepress having a press control circuit containing said series contacts andresponsive to closure of both said contacts for operating said press. 6.Control system as claimed in claim 5 in which said contact meansactuable by said shutter include a series pair of shutter contacTscloseable and openable with said shutter, said control circuit meansincluding a current path in which said series shutter contacts are inseries with said parallel relay coils, whereby closure of both saidshutter contacts is required for actuation of said relay coils. 7.Control system as claimed in claim 6 in which said start pulse circuitmeans includes a relay actuable by said photocell means and havingcontacts, said pair of relays of said press releasing circuit meanshaving respective further contacts in series, said press releasingcircuit means further including a holding current path for said pair ofrelays which includes said series further contacts thereof and furtherincludes a contact of said photocell actuable relay, said controlcircuit means including a further relay responsive to said photocellactuable relay for operating said shutter, means moveable in synchronismwith the working stroke of the press and press stroke contactsassociated therewith for completing said holding current path uponinitiation of the working stroke of the press.
 8. Control system asclaimed in claim 7 in which said means moveable in synchronism with theworking stroke of the press include a further contact, said controlcircuit including a current path to the shutter motor and containingsaid last mentioned contact for deenergizing said shutter motor uponinitiation of said working stroke of said press.
 9. Control system asclaimed in claim 7 including means coupling a contact of said photocellactuable relay in series in said holding current path of said pair ofpress releasing circuit means relays for breaking said holding currentpath upon interruption of the light curtain following starting of thepress, whereby to deenergize said pair of press releasing circuit meansrelays and stop said press.
 10. Control system as claimed in claim 9including a corrective contact member manually actuable after saidstopping of said press and means coupling contacts of said correctivecontact member in said shutter control circuit means, means defining acharging current path including a further contact of said manuallyactuable corrective contact member, said charging current path definingan additional start pulse circuit means responsive to deactuation ofsaid manually actuable corrective contact member and elimination of saidlight curtain interruption for, simultaneously with a subsequent closingof said shutter, once again applying operating current through saidseries pair of shutter contacts to said parallel press releasing circuitmeans relays to restart the press after an interruption of pressoperation by an interruption of the light curtain.
 11. Control system asclaimed in claim 10 in which said press releasing circuit means includesa normal press starting pulse path including a contact of said photocellresponsive relay, contacts of said pair of relays of said pressreleasing circuit means, and a contact of said shutter actuable contactmeans, said normal starting pulse path being coupled to the timing meanscapacitor associated with said press releasing circuit means fordischarging said capacitor therethrough.